Columnar structures

Columnar Structure and Grain Size. Most of the deposited films reported in the Hterature have a so-called columnar stmcture (see Fig. 

Due to the steric requirement of these substituents the formation of a columnar structure with infinite M M interactions is inhibited, and only the association of pairs of molecular units is allowed. The Ni Ni distance is 3.21 A [164]. If the same compound is crystallized in the presence of benzimidazole, the [Ni(dmg-BF2)2]2 dimer units are sandwiched between sheets of benzimidazole molecules due to n-n interactions resulting in an increased Ni Ni separation of 3.358 A [165]. With anthracene the n-n interactions seem to be stronger, because in this case the parent dimer molecule is cleaved. Each monomer now has a conformation of type B (Fig. 32) and is sandwiched by anthracene molecules [166]. Compound 121 has the same configuration [163d]. 

Fig. 21. The hydrogen-bonded hexameric unit that builds up the columnar structure of PhaSifOH, with hydrogen atoms omitted for clarity (304).

Fig. 14 Molecular arrangement in the crystal packing a and single ID columnar structure b in 27...

The inhomogeneous structure of the a-Si H films most likely leads to H2 motion that cannot be described as uniformly diffusive throughout the film. It has been suggested that H2 motion occurs along microvoids, present even in device quality films, that are aligned preferentially perpendicular to the films surface (Vanderheiden et al., 1987). These oriented microvoids can be considered as remnant micro-columnar structure in the films. The fact that the amount of H2 that can be reintroduced can never... 

Figure 6.2 Discotic molecules in a (a) nematic state ND, (b) twisted nematic discotic state Np (P/2 is half of cholesteric pitch), (c) columnar state, ordered D0 and disordered Dd, (d) hexagonal ordered columnar state Dho two-dimensional packing arrays for columnar structures in (e) hexagonal, Colh rectangular, Colr oblique, Col0b.

Ni-YSZ cermets deposited by RF sputtering (230 nm) were found to have micro-structural features consisting of columnar grains 13 to 75 nm long and 9 to 22 nm wide, and showed good adhesion to the YSZ layer on which they were deposited [128], In a three-layer Ni-YSZ-Ni film deposited on NiO by RF sputtering in another study, the YSZ layer exhibited a columnar structure with some pinholes [129], Microstructural and electrochemical features of Pt electrodes patterned by lithography on YSZ have also been studied [130,131]. 

The hardness, defined as the resistance to plastic deformation, of microporous silicon decreases with porosity p from the bulk silicon value of about 11.5 GaP to values around 4 GaP for porosities in the order of 75% following a (1-p)2/3 dependence. For porosities above 75% a further decrease in hardness is observed. The hardness of PS formed on highly doped p-type substrates is found to be somewhat less than that observed for low doped substrates, which may be caused by the more columnar structure of meso PS [Du5]. 

Figure 11.27 Schematic representation of the hexagonal columnar structure of an ABA triblock copolymer with a G1 dendron and the body-centered cubic stmcture of an ABA triblock with a G2 dendron.

A cylindrical hard deposit, which is grown on the tip of a cathode (A in Fig. 10.2.2), consists of two regions an inner fibrous black core and an outer gray hard shell (15). The inner core had a columnar structure that was made up of bundles of nanotubes and flocks of polyhedral graphitic particles (32). On the other hand, the hard shell was made of stacked graphitic flakes. 

Fibrous structures represent a grain refinement of columnar structure. Stress-relieving additives, eg, saccharin or coumarin, promote such refinement, as do high deposition rates. These may be considered intermediate in properties between columnar and fine-grained structures. 

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